Not Applicable.
The present invention relates generally to telecommunication systems and, more particularly, to wireless communication systems.
Wireless communication systems can send and receive data in a variety of ways. One type of wireless system utilizes time division multiple access (TDMA) techniques to provide communication channels for users of the network. As is well known to one of ordinary skill in the art, TDMA system data channels use the same set of carrier frequencies in different time slots so as to be orthogonal in the time domain. TDMA techniques allow multiple users to share the same frequency band by multiplexing transmissions in non-overlapping time slots. The total spectrum can be divided into frequency channels, each of which can be divided in time.
Known TDMA systems generally do not have a power control algorithm that can respond to rapid interference changes. In current TDMA systems, frequency reuse distance is implemented to ensure service (mainly voice) quality so that the capacity of such systems is usually not limited by interference.
With the recent development of so-called third generation (3G) wireless systems e.g. Enhanced General Packet Radio Services (EGPRS), tight frequency reuse, e.g. reuse frequency in every cell and every sector, has become increasingly important to improve the spectrum efficiency. In such systems, co-channel interference becomes the limiting factor of the system capacity and the service quality.
It would, therefore, be desirable to provide a wireless TDMA system having a power control scheme that responds to rapid interference variations. It would further be desirable to provide a TDAM system having a power control system that minimizes co-channel interference.
The present invention provides a TDMA system having first and second power control mechanisms. The first power control mechanism adjusts the power control target based upon a count of decoding errors during a decoding error-reporting period. The second power control mechanism adjusts the transmission power based upon a link quality measure for the previous link quality measurement period. This arrangement allows the TDMA system to respond effectively to rapidly changing interference conditions.
In one aspect of the invention, a wireless TDMA system receives a frame error indicator value from a receiver, e.g., mobile station, for the previous reporting period, which can correspond to a predetermined number of frames. In one embodiment, the receiver sets the frame error indicator to a first value when a predetermined threshold for the number of decoding errors is exceeded and a second value if the predetermined threshold is not exceeded. The receiver sends the frame error indicator value to the transmitter, which adjusts the power control target up or down for the next period based upon the value of the frame error indicator.
The transmitter also periodically receives a link quality measure from the receiver. In one embodiment, the receiver sends an average SINR level for a corresponding reporting period, which can be the same or different from the decoding error-reporting period. If the received SINR level is above a current target SINR level, the transmission power level is decreased for the next period. If the SINR level is below the current target SINR level, the transmission power level is increased for the next period.